Hybrid electric hydrogen fuel cell engine

ABSTRACT

A hybrid engine including features to meet aircraft thrust, passenger airflow, and fuel cell requirements. The engine includes a combustor burning the same fuel as the fuel cell. The engine has electric motors to utilize the power output of the fuel cell. The engine shafts have sprags to allow motors to drive the compressors and over run the turbines. The engine has variable flowpath geometry to bypass the combustor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. Section 119(e) ofcommonly-assigned U.S. Provisional Patent Application No. 63/137,900,filed Jan. 15, 2021, by Steve G. Mackin, Eric B. Gilbert, and Russell H.Higgins, entitled “HYBRID ELECTRIC HYDROGEN FUEL CELL ENGINE,” whichapplication is incorporated by reference herein.

BACKGROUND 1. Field

The present disclosure relates to propulsion systems and methods ofmaking the same.

2. Description of the Related Art

Aircraft typically include one or more engines to produce thrust. Thereare many different types or arrangements of engines, such as turbofanengines, turboprop engines, etc. These engines include a propulsor, suchas a fan or propeller, for producing thrust and an engine core, such asa gas turbine engine including turbines and compressors, that drives thepropulsor. A current trend in propulsor research is manufacturepropulsors that reduce or eliminate combustion of fossil fuels (e.g.,kerosene) so as to eliminate or reduce undesirable carbon emissions.Such propulsors include electric propulsors and hybrid propulsorsincluding a gas turbine engine and the electric propulsor used togetheror alternately. Hydrogen is a fuel with zero carbon emissions that canbe reacted in an electric propulsor comprising a fuel cell and aconventional gas turbine engine. However, conventional parallel hybridengines are not configured to assist in fuel cell operation andconventional electric propulsors require a large fuel cell and/or largebatteries to handle the larger power outputs required during takeoff andclimb of the aircraft. Moreover, burning hydrogen all the time in aconventional gas turbine engine can degrade the turbines. What isneeded, then, are improved propulsion systems that operate moreefficiently with reduced carbon emission. The present disclosuresatisfies this need.

SUMMARY

Illustrative, non-exclusive examples of inventive subject matteraccording to the present disclosure are described in the followingenumerated paragraphs:

A1. An aircraft propulsion system comprising:

a first compressor (e.g., LP compressor);

a second compressor (e.g., HP compressor) coupled to the firstcompressor to receive a first compressed air outputted from the firstcompressor and compress the first compressed air into a secondcompressed air;

a combustor positioned downstream of the second compressor to receivethe second compressed air outputted from the second compressor, thecombustor outputting a first exhaust gas formed from a fuel burned withthe second compressed air;

a turbine positioned downstream of the combustor to receive the firstexhaust gas;

a shaft connected to the turbine and the first compressor, the shafttransferring power from the turbine, driven by the first exhaust gas, tothe first compressor forming the first compressed air;

an HP electric motor connected to the second compressor; and

a fuel cell connected to the HP electric motor, the fuel cell configuredto react the second compressed air with the fuel to generate HP electricpower used to power the HP electric motor driving the second compressorto form the second compressed air.

A2. The aircraft propulsion system of paragraph A1, further comprising:

a generator connected to the first shaft to generate electric power fromthe power transferred from the turbine; and

a circuit transmitting the electric power from the generator to the HPelectric motor to power the HP electric motor driving the secondcompressor.

A3. The aircraft propulsion system of paragraph A1, further comprising:

a nacelle;

a duct between a core and the nacelle, the core comprising the secondcompressor, the combustor, and the turbine;

a fan coupled to the first compressor and the duct to draw:

-   -   a first portion of air into the duct to generate a second        exhaust outputted from the duct, the second exhaust providing a        thrust for an aircraft propelled using the aircraft propulsion        system, and    -   a second portion of the air into the first compressor, wherein        the first compressor compresses the second portion of the air to        form the first compressed air inputted to the second compressor.

A4. The aircraft propulsion system of paragraph A3, further comprising:

an LP electric motor;

a first LP shaft connected to the fan and the first compressor;

the shaft comprising a second LP shaft;

an LP clutch connected to the second LP shaft and the first LP shaft;and

a first configuration comprising the combustor burning the fuel to formthe first exhaust gas and the LP clutch connecting the first LP shaft tothe second LP shaft so that the first LP shaft and the second LP shafttransfer the power from the turbine, driven by the first exhaust gas, tothe first compressor and the fan; and

a second configuration comprising the fuel cell reacting the fuel withthe second compressed air, the LP clutch disengaging the first LP shaftfrom the second LP shaft, and the LP electric motor driving the fan andthe first compressor via the first LP shaft.

A5. The aircraft propulsion system of paragraph A4, further comprising:

one or more circuits; and

a computer system instructing:

-   -   activation of the second configuration during a cruise of the        aircraft, the second configuration further comprising the one or        more circuits electrically connecting the LP electric motor to        the fuel cell and the fuel cell powering the LP electric motor        via the one or more circuits, and    -   activation of the first configuration during a take-off of the        aircraft.

A6. The aircraft propulsion system of paragraph A1, further comprising:

an LP-HP clutch:

connecting the second compressor to the shaft during a take-off of anaircraft propelled using the aircraft propulsion system, wherein theturbine drives the second compressor via the shaft; and dis-engaging theshaft from the second compressor during a cruise of the aircraft.

A7. The aircraft propulsion system of paragraph A6, further comprising agearing connected to the second compressor to adjust a torque output ofthe turbine transferred to the second compressor.

A8. The aircraft propulsion system of paragraph A1, further comprising:one or more clutches:

dis-engaging at least one of the fan, the first compressor, or thesecond compressor from the shaft in a first configuration, the firstconfiguration further comprising:

the fuel cell reacting the fuel with the second compressed air togenerate electric power powering the electric motor driving the secondcompressor, and

the combustor not outputting an amount of first exhaust gas sufficientto generate thrust propelling an aircraft coupled to the aircraftpropulsion system;

coupling at least one of the fan, the first compressor, or the secondcompressor to the shaft in a second configuration further comprising:

the combustor burning the fuel with the second compressed air togenerate the first exhaust gas driving the turbine and

the turbine driving the second compressor via the shaft.

A9. The aircraft propulsion system of paragraph A8, wherein each of theclutches comprise a sprag clutch.

A10. The aircraft propulsion system of paragraph A9, further comprising:

a diverter regulating flow of the second compressed air outputted fromthe second compressor into the combustor or the fuel cell.

A11. The aircraft propulsion system of paragraph A10, wherein:

the diverter comprises a valve connected to at least one of the secondcompressor or the combustor,

the valve is open in the first configuration allowing output of thesecond compressed air to the combustor, and

the valve is closed in the second configuration blocking flow of thesecond compressed air to the combustor.

A12. The aircraft propulsion system of paragraph A11, wherein the valvecomprises a sleeve valve or a combustor inlet valve.

A13. The aircraft propulsion system of paragraph A10, further comprisinga nozzle directing the first exhaust gas to produce a thrust propellingthe aircraft, wherein:

the nozzle includes a variable core nozzle,

the diverter comprises the variable core nozzle or a variable turbinenozzle,

the diverter is open in the first configuration to allow flow of thefirst exhaust gas out of the nozzle to produce the thrust, and

the diverter is closed in the second configuration to divert the flow ofthe second compressed air to the fuel cell.

A14. The aircraft propulsion system of paragraph A10, wherein thediverter is positioned:

in the second compressor, or

downstream of the second compressor and upstream of the combustor.

A15. The aircraft propulsion system of paragraph A10, wherein thediverter comprises an adjustable vane in, or coupled to, the secondcompressor, the adjustable vane:

in the second configuration, diverting flow of the second compressed airto the fuel cell and blocking flow of the second compressed airdownstream to the combustor, and

in the first configuration, allowing flow of the second compressed airdownstream to the combustor.

A16. The aircraft propulsion system of paragraph A9, further comprising:

an engine bleed air system coupled to the second compressor;

the second configuration further comprising the engine bleed air systemconveying the second compressed air from the second compressor to thefuel cell, or

an aircraft system coupled to the engine bleed air system and the enginebleed air system conveying a first portion of the second compressed airto the fuel cell and a second portion of the second compressed air tothe aircraft system for pressurizing a cabin in the aircraft.

A17. The aircraft propulsion system of paragraph A16, further comprisingthe engine bleed air system:

coupled to at least one of the second compressor or the first compressorso as to obtain engine bleed air comprising at least a portion of thesecond compressed air or the first compressed air, coupled to at leastone of:

a low temperature heat exchanger configured to cool at least a portionof the engine bleed air to one or more temperatures suitable foraircraft use; or

a fuel heat exchanger configured to transfer heat from the engine bleedair to the fuel comprising liquid hydrogen, so that the heat boils theliquid hydrogen into a gas suitable for burning in the combustor orreaction in the fuel cell to generate the HP electric power.

A18. The aircraft propulsion system of paragraph A10, furthercomprising:

a nacelle;

a fan coupled to a core comprising the second compressor, the combustor,the turbine, and an HP turbine downstream of the combustor;

a duct between the core and the nacelle;

an LP electric motor connected to the fuel cell;

a plurality of shafts including a first LP shaft, the shaft comprising asecond LP shaft, a first HP shaft, and a second HP shaft;

the clutches including an LP clutch and an HP clutch;

the first configuration further comprising:

-   -   the LP clutch coupling the first LP shaft and the second LP        shaft,    -   the LP turbine, driven by the first exhaust gas, driving the        first compressor and the fan via the first LP shaft and the        second LP shaft,    -   the HP clutch coupling the first HP shaft and the second HP        shaft, and the HP turbine,    -   driven by the first exhaust gas in the first configuration,        driving the second compressor via the first HP shaft and the        second HP shaft; and

the second configuration further comprising:

the LP clutch dis-engaging the first LP shaft and the second LP shaftand the fuel cell powering the LP electric motor to drive the fan sothat the fan draws:

-   -   a first portion of air into the duct to generate a second        exhaust outputted from the duct, the second exhaust providing        thrust to an aircraft propelled using the aircraft propulsion        system, and    -   a second portion of the air into the first compressor so as to        form the first compressed air,

the HP clutch disengaging the first HP shaft from the second HP shaft,and the fuel cell powering the HP motor to drive the second compressorvia the first HP shaft.

A19. The aircraft propulsion system of paragraph A18, furthercomprising:

a computer instructing:

activation of the first configuration during at least one of a take-offor climb of the aircraft; and

activation of the second configuration during at least one of a cruise,taxiing, descent, or landing of the aircraft.

A20. The propulsion system of paragraph A18, wherein:

the fan comprises a plurality of first blades and the second compressorcomprises a plurality of second blades,

a computer controls a first angular velocity of the plurality of firstblades to generate the second exhaust needed for thrust during cruise ofthe aircraft, and

the computer controls a second angular velocity of the second blades soas to provide sufficient flow and pressure of the second compressed airto the fuel cell needed to generate electric power consumed by the HPelectric motor and LP electric motor during the cruise of the aircraftpowered using the second exhaust.

A21. The aircraft propulsion system of paragraph A20, wherein the secondcompressor has a number of compression stages tailored for providing thesufficient flow.

A22. The aircraft propulsion system of paragraph A18, further comprisinga gearing connected to the first LP shaft between the first compressorand the fan, the gearing adjusting a torque output of the LP electricmotor for driving the fan at a different speed than the firstcompressor.

A23. The aircraft propulsion system of paragraph A1, wherein the secondcompressor comprises at least one of a high pressure compressor or anintermediate pressure compressor, and the first compressor comprises alow pressure compressor.

A24. An aircraft comprising the aircraft propulsion system of paragraphA1, further comprising a fuel tank connected to the combustor and thefuel cell, wherein the aircraft propulsion system is configured togenerate thrust solely by reacting the fuel with the second compressedair in at least one of the combustor or the fuel cell.

A25. The aircraft of paragraph A24, wherein the fuel comprises hydrogen.

A26. The aircraft propulsion system of any of the paragraphs A1-A5,wherein:

the turbine comprises the single or only turbine in the aircraftpropulsion system and the propulsion system does not include anadditional HP turbine for driving the second compressor and/or theturbine is not sized or configured to mechanically drive the secondcompressor directly via an HP shaft.

A27. A method of generating thrust, comprising:

reacting a fuel using compressed air outputted from a compressor in ahybrid gas turbine engine, wherein the reacting is used to generate anexhaust gas providing thrust for an aircraft, the burning furthercomprising:

reacting the fuel in a fuel cell so as to generate electricity used topower at least one of:

-   -   a fan generating thrust during a cruise of the aircraft, or    -   a high pressure compressor during take-off of the aircraft; and        reacting the fuel in a combustor in the gas turbine engine        during take-off of the aircraft, so as to generate the exhaust        gas through combustion of the fuel.

A28. The method of paragraph A27, further comprising using the exhaustgas to generate electric power used to drive the compressor outputtingcompressed air to the combustor during a take-off of the aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a propulsor according to a first example.

FIG. 1B illustrates an example configuration of the propulsor of FIG. 1Aduring operation of the combustor (e.g., during take-off and/or climbingof an aircraft).

FIG. 1C illustrates an example configuration of the propulsor of FIG. 1Awhen the combustor is switched off (e.g., during cruise of an aircraft)and the propulsor is entirely powered using a fuel cell.

FIG. 2 illustrates an example propulsor comprising a non-coaxialarrangement of motors.

FIG. 3 illustrates an example propulsor including multiple clutches.

FIG. 4 illustrates an example propulsor including multiple turbines.

FIG. 5A illustrates an engine bleed air system coupled to a propulsor.

FIG. 5B illustrates an example configuration of the system of FIG. 5Aduring operation of the combustor (e.g., during take-off or climbing ofthe aircraft).

FIG. 5C illustrates an example configuration of the system of FIG. 5Bwhen the combustor is switched off (e.g., during cruise of the aircraft)and the propulsor is entirely powered by a fuel cell.

FIG. 6A is an enlarged view of an electric motor according to one ormore examples described herein.

FIGS. 6B and 6C are cross-sectional views of an overrunning (e.g.,sprag) clutch according to one or more examples described herein,wherein FIG. 6B illustrates the clutch engaging two shafts together andFIG. 6C shows the clutch disengaging the two shafts allowing one shaftto overrun the other shaft.

FIG. 7A illustrates positioning of a sleeve valve in a propulsoraccording to one or more examples described herein.

FIG. 7B illustrates an example sleeve valve.

FIGS. 8A and 8B illustrate an example diverter comprising a variablecore nozzle having adjustable nozzle walls, wherein FIG. 8A illustratesthe open configuration and FIG. 8B illustrates the closed configuration.

FIG. 8C illustrates an example HP compressor including rotor blades onrotor shaft and a diverter comprising adjustable vanes on a wall of thecore.

FIG. 9A-9D illustrate different views of an aircraft propelled using oneor more propulsors according to examples described herein.

FIG. 10 is a flowchart illustrating a method of making a propulsor,according to one or more examples.

FIG. 11 is a flowchart illustrating a method of operating a propulsor,according to one or more examples.

FIG. 12 illustrates a hardware environment for controlling the propulsoraccording to one or more examples described herein.

DESCRIPTION

In the following description, reference is made to the accompanyingdrawings which form a part hereof, and which is shown, by way ofillustration, several embodiments. It is understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present disclosure.

Technical Description

The present disclosure describes propulsion systems including one ormore electric motors driving one or more compressors utilizing the poweroutput of a fuel cell. The propulsion system includes one or more shaftscoupled to one or more clutches that allow the one or more electricmotors to drive the one or more compressors. Various examples of thepropulsion system provide a variable flowpath geometry to bypass thecombustor in various flight modes when the combustor is de-activated.

FIGS. 1A-1B illustrate aircraft propulsion system 100 according tovarious examples comprise a first compressor 102 and a second compressor104 coupled or connected to the first compressor 102 to receive a firstcompressed air 106 outputted from the first compressor 102. The firstcompressor 102 compresses air with a first compression ratio to form thefirst compressed air 106 and the second compressor 104 compresses thefirst compressed air 106 with a second compression ratio higher than thefirst compressor to form a second compressed air 108. Thus, the firstcompressor 102 comprises a low pressure compressor or lower pressurecompressor (hereinafter denoted LP compressor) outputting the firstcompressed air comprising a low pressure or lower pressure air (hereinafter LP compressed air). Furthermore, the second compressor 104 is ahigh pressure compressor or higher pressure compressor (hereinafterdenoted HP compressor) further compressing the LP compressed air 106into the second compressed air 108 comprising high pressure or higherpressure compressed air (hereinafter HP compressed air) having a higherpressure than the LP compressed air. In one example, LP compressor 102comprises a low pressure compressor (LPC, also known as a booster) andthe HP compressor 104 comprises an intermediate pressure compressor (IPcompressor) or a high pressure compressor (HPC).

The aircraft propulsion system 100 typically further comprises acombustor 110 positioned downstream of the HP compressor 104 to receivethe HP compressed air 108 outputted from the HP compressor 104. Thecombustor 110 is configured to output a first exhaust gas 112 formed asproduct of the combustion 162 of a fuel 114 using the HP compressed air108. Example fuels include, but are not limited to, hydrogen or otherfuel that is also combustible using the HP compressed air 108 in atleast one of a fuel cell 122 (to generate electric power) or thecombustor 110 to generate the first exhaust gas 112.

The propulsion system further comprises a nacelle 128; a duct 130between a core and the nacelle, the core comprising the HP compressor104, the combustor 110, and at least one turbine 116; and a fan 132coupled to the first compressor 102 and the duct 130. The fan 132 (e.g.,main engine fan) draws:

(1) a first portion 134 of air 136 into the duct 130 to generate asecond exhaust 138 outputted from the duct 130, the second exhaustproviding a fan thrust 140 to an aircraft propelled using the aircraftpropulsion system, and

(2) a second portion 142 of the air 136 into the first compressor 102(LP compressor), wherein the first compressor 102 compresses the secondportion 142 of the air 136 to form the first compressed air 106 inputtedto the second compressor 104 (HP compressor).

In various examples, the fan 132 is coupled to the LP compressor 102using a planetary gear 143 enabling the fan to be driven at a differentgear ratio (and speed) than the LP compressor 102.

The aircraft propulsion system further includes one or more electricmachines 120, 124 driving at least one of the HP compressor 104, the LPcompressor 102, and the fan 132 utilizing the power output of at leastone of fuel cell 122 or the at least one turbine 116. Example electricalmachines include, but are not limited to, at least one of amotor-generator, a motor coupled to a generator, a dynamotor, or amotor. The propulsion system further includes shafts coupled to one ormore clutches 144 (e.g., sprag clutches) that allow the electricmachines to drive the compressors and overrun the at least one turbine.In various examples, the shafts include a first shaft (LP shaft 1, 119)connecting the fan 132 and the LP compressor 102 to an LP electricmachine 124, a second shaft (LP shaft 2, 118) connected to the at leastone turbine 116, and an HP shaft 146 connecting a an HP electric machine(e.g., HP motor 120) to the HP compressor 104. In various examples, theone or more clutches include an LP clutch 144 connecting the LP shaft 1119 to the LP shaft 2 119. In some examples, LP shaft 1 (119) and LPshaft 2 (118) are each a single shaft. In other examples each of the LPshaft 1 and LP shaft comprise multiple shafts allowing connectionbetween the turbine 116, the first compressor 102, and the fan 132. Invarious examples, HP shaft 146 comprises a single shaft or multipleshafts connecting the HP electric machine to the HP compressor 104. Inone or more examples, the HP shaft 146 is positioned concentricallyabout a section of LP shaft 2 (118) so that LP shaft 2 passes through ahollow central portion of the HP shaft 146.

The aircraft propulsion system is configured for a hybrid (e.g.,parallel hybrid) propulsion operated in a combustor mode or anon-combustor mode. In the combustor mode, the combustor 110 combusts orburns the fuel 114 using the HP compressed air 108 to generatecombustion products comprising the first exhaust gas 112. During thenon-combustor mode, the combustor is de-activated or switched off (andnot burning the fuel) and one or more components of the aircraftpropulsion system (at least one of the fan 132, the first compressor102, and the second compressor 104) are driven using one or moreelectric machines 120, 124. Examples of operation phases or operationmodes of an aircraft propelled using the aircraft propulsion system inthe combustor mode include at least one of take-off or climbing of theaircraft. Examples of operation phases or modes of an aircraft propelledusing the aircraft propulsion system in the non-combustor mode includeat least one of taxiing, cruise, or descent of the aircraft.

The aircraft propulsion system 100 further includes a first nozzle 147downstream of the combustor 110 and the turbine 116 and exhausting thefirst exhaust gas 112. The first exhaust gas 112 outputted from thefirst nozzle 147 provides a core thrust 148 for an aircraft propelledusing the propulsion system. The propulsion system 100 includes one ormore diverters 157 (e.g., a variable turbine nozzle 145 a or variablecore nozzle 145 b) to bypass, regulate, or control (e.g., divert) aflowpath of the HP compressed air 108 at one or more locations in,downstream of, or at an output of, the HP compressor depending on theoperation mode of the aircraft. When the combustor 110 is switched off(non-combustor mode), the diverter 157 (e.g., nozzle 145 a, 145 bclosed) prevents or blocks flow the HP compressed air 108 at one or morelocations downstream of the HP compressor 104, enabling diversion of theHP compressed air 108 to the fuel cell 122. When the combustor isoperating (e.g., in combustor mode), the diverter 157 (e.g., open nozzle145 a, 145 b) allows flow of the HP compressed air 108 into thecombustor 110 and/or flow of the first exhaust gas out of the combustor110, through the turbine 116 and out of the first nozzle 147 to generatethe core thrust 148.

As used herein, the prefix HP is used to denote a part (e.g., shaft,compressor, clutch, or electrical machine) used in connection withdriving a higher pressure (HP) compressor 104 and the prefix LP is usedto denote a part (e.g., shaft, compressor, clutch, or electricalmachine) used in connection with driving a lower pressure (LP)compressor 102 or fan 132, such that the LP compressor 102 or fan 132outputs LP compressed air 106 having a lower compression or lowerpressure than the HP compressed air 108 outputted from the HP compressor104.

As used herein, driving or powering a motor, shaft, compressor, orturbine includes spinning the motor (or rotor of the motor), the shaft,or rotor shaft (including compressor blades) of the compressor, or rotorshaft (including turbine blades) of the turbine, respectively.

As used herein a fuel cell includes a device that reacts the fuel(comprising hydrogen or other fuel compatible with the fuel cell) usingat least a portion of the HP compressed air outputted from the HPcompressor to generate electricity comprising electric power. A fuelcell includes one or more fuel cells or a fuel cell stack.

As used herein, a clutch coupling two shafts includes the clutchconnecting (e.g., locking) the two shafts so that mechanical rotationalpower is transferred between the two shafts.

As used herein, two or more components may be described as being coupledor connected to one another. The desired definition is that element Acoupled to/connected to B is defined as either A directly or indirectlyconnected to B, including coupled or connected through one or moreintervening elements such as, but not limited to a clutch, e.g., theclutch transferring power between element A and element B when theclutch engages or couples element A to element B but not transferringpower between element A and element B when the clutch dis-engages orde-couples element A from element B.

Various examples of the propulsion system are described in the followingsections.

1. First Example Propulsion System

FIG. 1A-1C illustrate an example of the propulsion system 100 includingthe fan 132, LP compressor 102, the HP compressor 104, and combustor 110and wherein the turbine includes a single turbine 116 positioneddownstream of the combustor 110 to receive the first exhaust gas 112.When the LP clutch 144 couples LP shaft 1 (119) to the LP shaft 2 (118),LP shaft 1 and the LP shaft 2 transfer power from the turbine 116,driven the first exhaust gas 112, to the LP compressor 102 to powercompression of the air 136 into the LP compressed air 106 and power thefan 132 to draw the first portion 134 of the air 136 into the duct 130.

FIG. 1A-1C further illustrate the propulsion system 100 includes an LPelectrical machine 124 converting between electrical power andmechanical power. In one configuration, the first exhaust gas 112outputted from the combustor 110 drives the turbine 116 with mechanicalrotational power that is transferred via LP shaft 2 (118) and LP shaft 1(LP shaft 1 and LP shaft 2 coupled by the LP clutch 144) to the LPelectrical machine 124, and the LP electrical machine 124 (e.g.,comprising a generator) converts at least a portion of the mechanicalrotational power to electrical power that can be used to power one ormore aircraft systems (including the HP compressor, as discussed below).In this configuration, the LP electrical machine still allows transferof at least a portion of the mechanical rotational power via LP shaft 1(119) to drive the fan 132 and the LP compressor 102. In anotherconfiguration, the LP electric machine comprises a motor driving the fan132 and/or the LP compressor 102 when the LP clutch 144 dis-engages LPshaft 1 from LP shaft 2, thereby disconnecting the turbine 116 from thefan 132 and the LP compressor 102.

The propulsion system 100 further comprises an electric motor 120(designated HP motor) driving the HP compressor 104 via the HP shaft 146so that the HP compressor 104 compresses the LP compressed air 106 intothe HP compressed air 108. The HP motor 120 is powered (or driven) bythe electric power generated in at least one of the LP electric machine124 or the fuel cell 122. As described above, the LP electric machine124 is configured to convert at least a portion of the mechanicalrotational power transferred from the turbine to the electrical powerfor powering the HP motor 120. In another example, the fuel cell 122reacts the fuel 114 using at least a portion of the HP compressed air108 outputted from the HP compressor 104 to generate the electric powerpowering the HP motor 120 to drive HP compressor 104. One or morecircuits 126 controlled by one or more computers or controllers 156control transmission of the electric power from the fuel cell and/or theLP electrical machine 124 to drive the HP motor 120.

FIG. 1A-1C further illustrates the propulsion system 100 includes a fuelvalve 155 controlling flow of the fuel 114 along fuel lines from a fueltank 150 and into the fuel cell 122 or the combustor 110. In the exampleshown, the fuel 114 comprises hydrogen stored in the tank comprising aliquid hydrogen storage tank 150 and fuel heat exchanger 154 is coupledto the compressor bleed outlet of the first compressor 102 or the secondcompressor 104 so as to boil the liquid hydrogen into gas suitable to beburned in the combustor or reacted in the fuel cell. Specifically, thefuel heat exchanger 154 transfers heat from hot compressor offtakes(outputting a tapped portion of the first compressed air 106 and/or atapped portion of the second compressed air 108) to boil the fuel intothe gas. Also shown is a low temperature heat exchanger 152 used to coolthe tapped portion of the hotter first compressed air 106 or the tappedportion of hotter second compressed air 108 to a temperature suitablefor aircraft use (e.g., in the cabin or air conditioning system). Invarious examples, the compressor bleed outlet comprises a hot compressorofftake including or coupled to an engine bleed air system. FIG. 1Afurther illustrates a cooling loop 153 used to precool the compressedair 108, 106 or to cool hot engine components.

The propulsion system further includes a second nozzle 149 to exhaust160 water or water vapor outputted from the fuel cell 122, the water orwater vapor comprising a product of the reaction of the hydrogen and theHP compressed air 108 in the fuel cell 122. The exhaust 160 is cooled ina fuel cell heat exchanger 154 by combination with a portion of the LPcompressed air 106 outputted from the LP compressor 102. The exhaust 156through the second nozzle 149 provides supplemental or additional thrust159 for the aircraft powered by the propulsion system 100.

a. Example Propulsion System Operation During Combustor Mode

FIG. 1B illustrates an operation of the propulsion system 100 during thecombustor mode when the combustor 110 is burning the fuel 114 using theHP compressed air 108 so as to form the first exhaust gas 112 drivingthe turbine 116. The LP clutch 144 couples LP shaft 2 (118) to the LPshaft 1 (119) so that the turbine 116 drives the LP compressor 102 andthe fan 132 via the LP shaft 1 and LP shaft 2. As a result, most or allof the power powering LP compressor 102 and the fan 132 is generatedfrom the first exhaust gas 112 driving the turbine 116. The LP shaft 2driven by the turbine 116 also drives the LP electrical machine 124 togenerate the electric power (converted from the mechanical rotationalpower received from the turbine 116) used to power the HP motor 120. TheHP motor 120 drives the HP compressor 104 via the HP shaft 146. In someexamples, supplemental electric power from the fuel cell 122 is alsoused to power the HP motor 120 driving the HP compressor. As illustratedin FIG. 1B, the one or more diverters 157 (comprising variable corenozzle 145 b and/or variable turbine nozzle 145 a) are open to allowflow of the first exhaust gas 112 out of the first nozzle 147 to providethe core thrust 148.

b. Example Propulsion System Operation During Non Combustor Mode(Electric Mode)

FIG. 1C illustrates an operation of the propulsion system 100 in anon-combustor mode (electric mode) when the combustor 110 is switchedoff. Flow of the fuel 114 to the combustor is switched off by the fuelvalve 155 and flow of the HP compressed air 108 at one or more locationsdownstream of the HP compressor is blocked by the diverter 157 (e.g.,closure of nozzle 145 a, 145 b). The HP compressor 104 is driven by theHP electric motor 120 powered by the fuel cell 122. The LP clutch 144de-couples (e.g., disengages) LP shaft 2 (118) from LP shaft 1 (119) sothat the LP compressor 102 and the fan 132 are driven by the LPelectrical machine 124 via LP shaft 1 (119), e.g., overrunning LP shaft2).

2. Second Example: Non-Coaxial Arrangement of the Electrical Machines

FIG. 2 illustrates a propulsion system 200 comprising a non-coaxialarrangement 201 of the LP electrical machine 124 and the HP motor 120.The HP motor 120 drives the HP shaft 146 via HP drive shaft 203 and HPgear box 204, and the LP electrical machine 124 drives LP shaft 1 (119)via LP drive shaft 206 and LP gear box 208. In the example shown, the LPclutch 144 is located on a section of the LP shaft 1 (119) downstream ofthe combustor 110. In one or more examples, the non-coaxial arrangement202 is configured to shorten a length of the propulsion system and/orimprove a flow path of the LP compressed air 106 and HP compressed air108 through the propulsion system 200.

3. Third Example: Multiple Clutch Propulsion System

FIG. 3 illustrates a propulsion system 300 including the fan 132, firstcompressor 102, second compressor 104, combustor 110, turbine 116, fuelcell 122, HP motor 120, and at least one of an LP to HP gearbox 302 orLP-HP clutch 304 connecting the LP shaft 2 (118) and the HP shaft (146).In various examples, the LP to HP gearbox 302 includes the LP-HP clutch304 and a gearing system. In one example, the LP to HP gearbox 302 orLP-HP clutch 304 connects sections of the LP shaft 2 (118) and HP shaft146 in the HP compressor 104 or between the combustor 110 and the HPcompressor 104. The LP-HP clutch 304:

(1) de-couples or dis-engages the HP shaft 146 from the LP shaft 2 (118)allowing the HP shaft 146 to overrun the LP shaft 2 (118) duringoperation of the propulsion system 100 in the non-combustor mode, and

(2) couples or engages the HP shaft 146 to the LP shaft 2 (118) so thatthe HP shaft 146 is driven by the turbine 116 via LP shaft 2 (118) whenthe turbine 116 is actively being driven by the first exhaust gas 112during combustor mode operation of the propulsion system 300.

In various examples, the LP-HP clutch 304 comprises a sprag clutch. Insome examples, a configuration of the propulsion system 300 includingthe LP-HP clutch 304 enables the HP motor 120 to be significantlydownsized while avoiding the need for a second turbine (HP turbine).

4. Fourth Example: Propulsion System Including Multiple Turbines

FIG. 4 illustrates an aircraft propulsion system 400 according to afourth example comprising the LP compressor 102, HP compressor 104,combustor 110, a first turbine 116 (e.g., LP turbine), LP shaft 1 (119),LP shaft 2 (118), LP clutch 144 connecting LP shaft 1 and LP shaft 2; asecond turbine 402 (e.g. HP turbine) positioned downstream of thecombustor to receive the first exhaust gas (LP turbine 116 downstream ofHP turbine); a first HP shaft 146 connecting the HP motor to the HPcompressor, and a second HP shaft 444 (HP shaft 2) connecting the HPturbine to the HP shaft 2 via an HP clutch 446.

When the combustor 110 is burning fuel 114 and generating first exhaustgas 112 in the combustor mode, the HP clutch 446 couples the HP shaft 2(444) to HP shaft 1 (146) and the LP clutch 144 couples the LP shaft 1(119) to the LP shaft 2 (118) so that:

(1) the HP turbine 402, driven by the first exhaust gas 112, drives theHP compressor 104 via HP shaft 2 (444) and HP shaft 1 (146); and

(2) the LP turbine 116, driven by the first exhaust gas 112, drives theLP compressor 102 and the fan 132 via LP shaft 1 (119) and LP shaft 2(118).

The propulsion system further includes the LP electric machine 124comprising an LP motor 403. When the combustor is de-activated(non-combustor mode or electric mode):

(1) the LP clutch 144 de-couples (or dis-engages) LP shaft 1 (118) fromLP shaft 2 (119) and the LP motor 403 drives the fan 132 and the LPcompressor 102 via LP shaft 1 (e.g., overrunning LP shaft 2), and

(2) the HP clutch 446 de-couples or disengages the HP shaft 1 (146) fromthe HP shaft 2 (444) and the HP motor 120 drives the HP compressor 104via HP shaft 1 (e.g., overrunning HP shaft 2).

The LP motor 403 and the HP motor 120 are powered using the electricpower generated in the fuel cell 122 reacting the fuel using the HPcompressed air 108.

5. Fifth Example: Connection to an Engine Bleed Air System

FIG. 5A illustrates the aircraft propulsion system of FIG. 4 furthercomprising an engine bleed air system 500 coupling the HP compressor 104to the fuel cell 122 and/or an aircraft system. The engine bleed airsystem 500 includes one or more conduits 502, one or more engine bleedair ports 504, 506, and one or more engine bleed valves 508 regulatingflow of the HP compressed air 108 from the HP compressor 104 through theconduits 502 to the fuel cell 122 and/or the aircraft system. FIG. 5Aillustrates an example wherein the engine bleed ports comprise a firstport 504 positioned aft of a second port 506, the second port 506positioned to receive a lower pressure portion of the HP compressed air108 and the first port 504 positioned to receive a higher pressureportion of the HP compressed air 108 (the higher pressure portion havinga pressure higher than the lower pressure portion of the HP compressedair, e.g., because the higher pressure portion is outputted from acompressor stage (in the HP compressor) aft or downstream of the secondport 506. The engine bleed air valves 508 include a first valve 508 acontrolling flow of the HP compressed air 108 into the engine bleed airsystem 500 from the first port 504 and a second valve 508 b controllingflow of the HP compressed air 108 into the engine bleed air system 500from the second port 506. In this way, the pressure of the HP compressedair 108 diverted to the engine bleed air system is regulated dependingon a phase of flight. For example, during combustion mode operation(e.g., during take off), the first valve 508 a closed and the secondvalve 508 b is open to allow transfer of the lower pressure portion ofthe HP compressed air 108 into the engine bleed air system. In anotherexample (e.g., during idle of the combustor or non-combustion mode), thefirst valve 508 a is open and the second valve 508 b are open to allowtransfer of the higher pressure portion of the HP compressed air intothe engine bleed air system 500.

Operation of the engine bleed air system 500 is illustrated in thefollowing sections with reference to the fourth example. However, theengine bleed air system 500 is configurable to operate with any of theexamples (e.g., first example, second example, and third example)described herein.

a. Operation when Combustor is Burning or Combusting Fuel (CombustionMode)

FIG. 5B illustrates operation of the fourth example when the combustor110 is burning (or combusting) fuel 114 and outputting the first exhaustgas 112 driving the LP turbine 116 and the HP turbine 402. The LP clutch144 couples or engages LP shaft 1 (119) to LP shaft 2 (118) so that LPturbine 116 is coupled to and drives the fan 132 and the LP compressor102 via LP shaft 1 and LP shaft 2. The HP clutch 446 couples HP shaft 1(146) to HP shaft 2 (444) so that the HP turbine 402 is coupled to anddrives the HP compressor 104 via HP shaft 1 and HP shaft 2. The diverter157 (e.g., nozzle 145 a, 145 b) is open to allow flow of the firstexhaust gas 112 from the combustor 110, through the HP turbine 402 andthe LP turbine 116, and out the first nozzle 147 to generate the corethrust 148. The engine bleed valve 508 b is open to allow flow of the HPcompressed air 108 through the engine bleed air system 500 to anaircraft system (e.g., the aircraft cabin via air conditioning orpressurizing system) and/or the fuel cell 122. The fuel cell 122 reactsthe fuel 114 using the HP compressed air 108 received through the enginebleed air system 500 to generate electric power powering the LP motor403 and/or the HP motor 120. In some examples, the LP motor 403 poweredby the fuel cell 122 provides additional power for driving the fan 132and the LP compressor 102 (in addition to the mechanical power suppliedby the LP turbine 116). In yet further examples, the HP motor orelectric machine 120 is driven by the HP turbine 402 via HP shaft 1 andHP shaft 2 and operates in generator mode to output electric power usedto supply various aircraft systems.

b. Operation when Combustor is Deactivated (Non-Combustor Mode orElectric Mode)

FIG. 5C illustrates operation of the fourth example when the combustor110 is switched off and not burning the fuel 114. The diverter 157(e.g., variable nozzle 145 a, 145 b is closed) to block flow the HPcompressed air 108 to one or more locations downstream of the HPcompressor. The LP clutch 144 de-couples or dis-engages the LP shaft 1from LP shaft 2 (de-coupling the LP compressor 102 from the LP turbine116) and the HP clutch 446 de-couples or disengages the HP shaft 1 fromHP shaft 2 (de-coupling the HP compressor 104 from the HP turbine 402).The HP motor 120, entirely powered using electric power from the fuelcell 122, drives (e.g., spins) the HP compressor 104 via HP shaft 1(e.g., overrunning HP shaft 2). The LP motor 403, also entirely poweredusing electric power from the fuel cell 122, drives (e.g., spins) thefan 132 and the LP compressor 102 via LP shaft 1 (e.g., overrunning LPshaft 2).

FIGS. 5B and 5C further illustrate the output 418 of the engine bleedair system 500 outputting the engine bleed air 550 comprising a portion516 of the second compressed air 108. In some examples, the output 418is coupled to the fuel heat exchanger 154 and the fuel heat exchanger154 transfers heat of the hotter portion 516 to boil the fuel 114 (e.g.,liquid hydrogen outputted from the tank 150) into a gas suitable to beburned in the combustor 110 or reacted in the fuel cell 122. In anotherexample, the output 418 is coupled to the low temperature heat exchanger152 and the low temperature heat exchanger 152 uses colder fuel 114 tocool the portion 516 of second compressed air 108 to a lower temperaturesuitable for aircraft use (e.g., by an air conditioning system supplyingair derived from the second compressed air 108 to the cabin).

6. Example Clutches

FIG. 6A shows an enlarged view of an electric machine (HP motor, LPmotor, or LP moto-generator), a first drive shaft 119, 146 (HP shaft 1or LP shaft 1), a second drive shaft 118, 444 (HP shaft 2 or LP shaft2), and the clutch 144, 446, 304 (LP clutch, HP clutch, or LP-HPclutch). In the illustrated example, the electric machine 120, 124includes an armature 600 coupled to the first drive shaft 119 and astator 602 surrounding the armature 600. The armature 600 may be formedunitarily with the first drive shaft 119. The armature 600 may includecoils and the stator 602 may include magnets (or electromagnets), orvice versa. When the electric motor 120, 124 is energized (e.g., via thecontroller 156), the armature 600 rotates, thereby rotating the firstdrive shaft 119, 146. When the electric motor 120, 124 is de-energizedthe armature 600 no longer functions as the primary driver of driveshaft 119. However, the armature 600 and therefore, the second driveshaft 119 are still free to rotate within the stator 602. In someexamples, the LP electric motor 124 operates as a generator to power theHP motor 120 and/or provide electrical power directly to one or moreelectrical system(s) of the aircraft. The electric motor 120, 124 can beimplemented as any type of electric motor (e.g., an induction motor, aDC/AC permanent magnet motor, etc.) and is not limited to the exampleelectric motor 120, 124 shown in FIG. 6A. Instead, it is understood thatother types of electric motors can be similarly used, and the armature,stator, commutator, etc. may be arranged differently depending on thetype of motor.

In the illustrated example, the overrunning clutch 144, 446, 304 isimplemented as a sprag clutch 604. The sprag clutch 604 includes anouter race 606, an inner race 608, and a plurality of movable sprags 610disposed between the outer race 606 and the inner race 608. In thisexample, the second drive shaft 118 (which is powered by the combustor110 via a turbine (FIG. 1A)) is coupled to the outer race 606 and thefirst drive shaft 119 (which is coupled to the fan 132 (FIG. 4 )) iscoupled to the inner race 608. FIGS. 6A and 6B are cross-sectional viewsof the example overrunning clutch 144, 446, 304. The sprags 610 (one ofwhich is referenced in each figure) are pivotable about their centers(extending into the page). In FIG. 6A, the outer race 606 is rotating inthe clockwise direction. This occurs during the combustion mode ofoperation when the combustor 110 is and the first exhaust gas is drivingthe turbine 116. The interaction between the outer race 606 and thesprags 610 causes the sprags 610 to pivot into and engage the inner race608. As a result, the outer race 606, the sprags 610, and the inner race608 all rotate together, in the clockwise direction. Therefore, when thesecond drive shaft 118 rotates the outer race 606, the outer race 606rotates the inner race 608 and, thus, rotates the first drive shaft 119in the same direction. In FIG. 6B, the inner race 608 is rotating in theclockwise direction independent of the outer race 606. This occurs, forexample, during the non-combustion (electric) operation when thecombustor 110 is off and the electric motor 120, 124 is instead drivingthe first drive shaft 119. As shown in FIG. 6B, the inner race 608slides along the inner surfaces of the sprags 610. However, thisinteraction does not cause the sprags 610 to frictionally engage theouter race 606. As such, the inner race 608 rotates in the clockwisedirection without causing rotation of the outer race 606. If the outerrace 606 is rotated up to match the rotational speed of the inner race608, the sprags 610 are rotated into the inner race 608 and the outerrace 606 eventually overdrives the inner race 608. As such, the innerrace 608 rotates at least as fast as the outer race 606. Conversely,while the outer race 606 is rotating, the inner race 608 can be rotatedindependently at a faster rotational speed, which does not affect theouter race 606. The overrunning clutch 144 advantageously enables thecombustor 110 and the electric motor 120 to independently drive thepropulsor 100 without additional actuating components that are found inother types of clutches.

7. Example Diverters

FIGS. 7A and 7B illustrate an example diverter comprising an sleevevalve 700 comprising two adjacent plates 702 positioned (e.g., in a lowMach region of) the flow of the HP compressed air 108 or first exhaustgas in the propulsion system. The plates have holes 704:

(1) aligned (by rotation 706 of the plates 702 relative to one another)to allow flow of the first exhaust gas or the HP compressed air or thefirst exhaust gas through the holes during combustor mode operation ofthe propulsor 100, or

(2) mis-aligned (by the rotation 706) to block flow of the first exhaustgas 112 or the HP compressed air through the holes during thenon-combustor mode (electric mode) of operation of the propulsor 100.FIG. 7A illustrates and example wherein the sleeve valve 700 isconnected to an output of the HP compressor 104 or to an input or inletof the combustor 110.

FIGS. 8A and 8B illustrate an example diverter 157 comprising a variablecore nozzle 800 having adjustable nozzle walls 802. FIG. 8A illustratesthe open configuration wherein the nozzle walls 802 are substantiallyparallel to the flow of the first exhaust gas 112 to allow substantiallyunobstructed flow of the first exhaust gas 112 outputted from thecombustor 110 when the combustor is burning the fuel using the HPcompressed air 108 in the combustor mode. FIG. 8B illustrates the closedconfiguration wherein the nozzle walls 802 are angled into the flowdirection of the HP compressed air 108 to block flow of the HPcompressed air 108 downstream of the HP compressor, enablingre-direction of the HP compressed air 108 for combustion with fuel 114in the fuel cell 122 generating electrical power powering the LPcompressor 102, the HP compressor 104, and the fan 132. In one or moreexamples, the variable core nozzle 800 is selected and configured toreduce aerodynamic drag.

FIG. 8C illustrates an example HP compressor 104 including rotor blades810 driven by a rotor shaft 812 (the rotor shaft 812 driven by HP motor120) and a diverter 157 comprising adjustable vanes 814 on a wall 816 ofthe core. In this example, the adjustable vanes (e.g., de-swirl vanes)are movable

(1) to allow flow of the HP compressed air 108 downstream of the vanes814 when the vanes are in an open position during operation of thepropulsor in the combustion mode, or

(2) into the flow so as to block flow of the HP compressed airdownstream of the engine bleed air system 500 when the vanes are in aclosed position during operation of the propulsor in the non-combustionmode or electric mode.

8. Example Compressor and Electrical Machine Configurations

In various examples, the HP motor driven by the fuel cell enablesvarious modifications of the configuration of, or the size and number ofvarious components in, the propulsor 100.

In one or more examples, the LP electric machine drives the LPcompressor and/or the HP motor drives the HP compressor to output the HPcompressed air having a pressure tailored for optimal functioning of thefuel cell and other aircraft systems (other than the propulsor or thecombustor 110). In one or more examples, the air pressure required forcombustion in the fuel cell or the aircraft system is lower (e.g., 45psi) as compared to the capability of the LP compressor and HPcompressor and the air pressure needs for combustion in the combustor(e.g., ˜160 psi). However, since the LP compressor and the HP compressorare decoupled from the turbines during non-combustion mode operation,the electric machines can spin the compressors at the optimum ortailored speed for fuel cell air production or other air pressure needsof various aircraft systems.

In various examples, the compressors and turbine(s) each include one ormore compression stages or turbine stages that are sized for differentengine configurations including the HP motor. For example, the presenceof the HP motor driving the HP compressor allows reduction of the numberof, the size of, and the number of compression stages in the compressorand/or the number of turbine stages in the turbine(s) because at leastsome of the power for driving the HP compressor is derived from the fuelcell instead of the turbines. In some examples, at least one of thenumber of turbines, the size of the turbine, and the number of turbinestages in the turbine are selected to be sufficient to power the fan, LPcompressor, and provide the electrical power to one or more aircraftsystems (including the HP motor), but not the HP compressor.

In yet further examples, at least one of the size (or number of blades)in the fan, the number of compressor stages in each of the HP compressorand the LP compressor, or the bypass ratio (the amount of air drawn intothe duct as compared to into the core) are tailored so that the fanproducing the second exhaust gas provides all the thrust during cruiseof the aircraft.

In one or more examples, the HP motor drives the HP compressor at highervelocities (i.e., the HP compressor blades on the HP rotor shaft in theHP compressor are driven at higher angular velocity) as compared to theHP compressor driven by an HP turbine. In other examples, the turbine isconfigured to spin LP shaft 1 and LP shaft 2 at higher velocitiestailored for increased efficiency performance of the LP compressor(independent of the velocity requirements of the HP compressor) sincethe HP compressor is driven separately by the HP motor. In yet furtherexamples, the one or more circuits control the transfer of electricalpower so that the HP motor drives the HP compressor at different speedsthan the LP compressor, the speed of the HP compressor specificallytailored for different phases of the flight (take off, cruise, highaltitude cruise, descent etc.).

In yet further examples, powering the HP motor using a fuel cell reducesthe required size of the HP motor (i.e., reduces the number of windingsor coils) as compared to the HP motor driven entirely by a generator(because in some examples, generators operate at higher voltages thanthe fuel cell). In other examples, the LP electrical machine isconfigured (e.g., sized, including the number of windings in thegenerator and motor) to output the electrical power requirements of theHP compressor and LP compressor and fan during the various phases ofoperation of the aircraft.

9. Example Aircraft Including the Propulsion Systems

FIG. 9A-9D illustrate an aircraft 900 coupled to a propulsion system100, 200, 300, 400, including fuel cell 122 (e.g., comprising a fuelcell stack 904) and motor controller 156, liquid hydrogen tank 150, andaircraft systems (e.g., thermal management system 902 and powerconditioner 906).

10. Example Process Steps Method of Making

Block 1000 represents providing a first compressor (e.g., LPC).

Block 1002 represents coupling a second compressor (e.g., HPC) to thefirst compressor so as to receive a first compressed air outputted fromthe first compressor the second compressor compressing the firstcompressed air to form a second compressed air.

Block 1004 represents positioning a combustor downstream of the secondcompressor to receive the second compressed air outputted from thesecond compressor, the combustor outputting a first exhaust gas formedfrom a fuel burned with the second compressed air.

Block 1006 represents positioning a least one turbine downstream of thecombustor to receive the first exhaust gas.

Block 1008 represents coupling a fan to the first compressor to draw:

a first portion of air into the duct to generate a second exhaustoutputted from the duct, the second exhaust providing a thrust to anaircraft propelled using the aircraft propulsion system, and

a second portion of the air into the first compressor, wherein the firstcompressor compresses the second portion of the air to form the firstcompressed air inputted to the second compressor.

Block 1010 represents connecting one or more electric machines drivingthe compressor(s) (to form the compressed air) and the fan, andconnecting a fuel cell and one or more electric circuits and controllersto the electric machines for powering the electric machines. The one ormore circuits and controllers control flow of the electric power betweenthe fuel cell and the electric machines.

In one or more examples, the step comprises selecting a size, weight andpower rating of the fuel cell for use during cruise (not as the mainpower supply during take-off), so that the fuel cell is smaller,lighter, and has smaller power output than a fuel cell sized forproviding all the power to the propulsor during take-off. In one or moreexamples, high power demand is met by burning fuel in the combustor.

Block 1012 represents connecting one or more shafts coupling the turbineto the first compressor and the fan, coupling an electric machine to thesecond compressor, and optionally coupling an electric machine to thefan and the first compressor.

Block 1014 represents providing a nacelle and a duct between a core andthe nacelle, the core comprising the second compressor, the combustor,and the turbine, and the nacelle housing the core and the fan.

Block 1016 represents the end result, a propulsor for an aircraft ordrone. Illustrative, non-exclusive examples of inventive subject matteraccording to the present disclosure are described in the followingenumerated paragraphs:

A1. An aircraft propulsion system (100, 200, 300, 400) comprising:

a first compressor (102) (e.g., LP compressor (102));

a second compressor (104) (e.g., HP compressor (104)) coupled to thefirst compressor (102) to receive a first compressed air (106) outputtedfrom the first compressor (102) and compress the first compressed air(106) into a second compressed air (108);

a combustor (110) positioned downstream of the second compressor (104)to receive the second compressed air (108) outputted from the secondcompressor (104), the combustor (110) outputting a first exhaust gas(112) formed from a fuel (114) burned with the second compressed air(108);

a turbine (116) positioned downstream of the combustor (110) to receivethe first exhaust gas (112);

a shaft (118) connected or coupled to the turbine (116) and the firstcompressor (102), the shaft (118) transferring power (e.g. mechanicalpower) from the turbine (116), driven by the first exhaust gas (112), tothe first compressor (102) forming the first compressed air (106);

an HP electric motor (120) connected to or coupled to the secondcompressor (104);

a fuel cell (112) connected to (e.g., electrically coupled to) the HPelectric motor (120), the fuel cell (122) configured to react the secondcompressed air (108) with the fuel (114) to generate HP electric powerused to power the HP electric motor driving the second compressor (104)to form the second compressed air (108).

A2. The aircraft propulsion system (100, 200, 300, 400) of paragraph A1,further comprising:

a generator (124) connected or coupled to the first shaft to generateelectric power from the power transferred from the turbine (116); and

a circuit (126) transmitting the electric power from the generator (124)to the HP electric motor (120) to power the HP electric motor (120)driving the second compressor (104).

A3. The aircraft propulsion system (1200) (100, 200, 300, 400) of any ofthe paragraphs A1-A2, further comprising:

a nacelle (128);

a duct (130) between a core and the nacelle (128), the core comprisingthe second compressor (104), the combustor (110), and the turbine (116);

a fan (132) (e.g., main engine fan) coupled to the first compressor(102) and the duct (130) to draw:

-   -   a first portion (134) of air (136) into the duct (130) to        generate a second exhaust (138) outputted from the duct (130),        the second exhaust (138) providing a thrust (140) (e.g., fan        thrust) for an aircraft (900) propelled using the aircraft        propulsion system (100, 200, 300, 400), and    -   a second portion (142) of the air (136) into the first        compressor (102), wherein the first compressor (102) compresses        the second portion (142) of the air (136) to form the first        compressed air (106) inputted to the second compressor (104).

A4. The aircraft propulsion system (100, 200, 300, 400) of any of theparagraphs A1-A3, further comprising:

an LP electric motor (124);

a first LP shaft (119) connected to the fan (132) and the firstcompressor (102);

the shaft (118) comprising a second LP shaft (118);

an LP clutch (144) connected to the second LP shaft (118) and the firstLP shaft (119); and

a first configuration comprising the combustor burning the fuel to formthe first exhaust gas 112 and the LP clutch (144) connecting the firstLP shaft (119) to the second LP shaft (118) so that the first LP shaft(119) and the second LP shaft (118) transfer the power from the turbine(116), driven by the first exhaust gas (112), to the first compressor(102) and the fan (132); and

a second configuration comprising the fuel cell reacting the fuel (114),the LP clutch disengaging the first LP shaft (119) from the second LPshaft (118), and the LP electric motor (124) driving the fan (132) andthe first compressor (102) via the first LP shaft (119).

A5. The aircraft propulsion system (100, 200, 300, 400) of paragraph A4,further comprising:

one or more circuits (126); and

a computer (1202) system (1200) instructing:

-   -   activation of the second configuration during a cruise of the        aircraft, the second configuration further comprising the one or        more circuits (126) electrically connecting the LP electric        motor (124) to the fuel cell (122) and the fuel cell (122)        powering the LP electric motor (124) via the one or more        circuits (126), and    -   activation of the first configuration during a take-off of the        aircraft.

A6. The aircraft propulsion system (100, 200, 300, 400) of any of theparagraphs A1-A6, further comprising:

an LP-HP clutch (446):

connecting the second compressor (104) to the shaft (118) during atake-off of an aircraft (900) propelled using the aircraft propulsionsystem (100, 200, 300, 400), wherein the turbine (116) drives the secondcompressor (104) via the shaft (118); and

dis-engaging the shaft (118) from the second compressor (104) during acruise of the aircraft (900).

A7. The aircraft propulsion system (100, 200, 300, 400) of paragraph A6,further comprising a gearing connected to the second compressor (104) toadjust a torque output of the turbine (116) transferred to the secondcompressor (104).

A8. The aircraft propulsion system (100, 200, 300, 400) of any of theparagraphs A1-A8,

further comprising: one or more clutches (144):

dis-engaging at least one of the fan (132), the first compressor (102),or the second compressor (104) from the shaft (118) in a firstconfiguration, the first configuration further comprising:

the fuel (114) cell reacting the fuel (114) with the second compressedair (108) to generate electric power powering the electric motor (120)driving the second compressor (104), and

the combustor (110) not outputting an amount of first exhaust gassufficient to generate thrust propelling an aircraft coupled to theaircraft propulsion system;

coupling at least one of the fan (132), the first compressor (102), orthe second compressor (104) to the shaft (118) in a second configurationfurther comprising:

the combustor (110) burning the fuel (114) with the second compressedair (108) to generate the first exhaust gas (114) driving the turbine(116) and

the turbine (116) driving the second compressor (104) via the shaft(118).

A9. The aircraft propulsion system (100, 200, 300, 400) of paragraph A8,wherein each of the clutches (144, 304, 446) comprise a sprag clutch.

A10. The aircraft propulsion system (100, 200, 300, 400) of any of theparagraphs A1-A9, further comprising:

a diverter (157) regulating flow of the second compressed air (108)outputted from the second compressor (104) into the combustor (110) orthe fuel (114) cell.

A11. The aircraft propulsion system (100, 200, 300, 400) of paragraphA10, wherein:

the diverter (157) comprises a valve (700) connected to at least one ofthe second compressor (104) or the combustor (110),

the valve (700) is open in the first configuration allowing output ofthe second compressed air (108) to the combustor (110), and

the valve (700) is closed in the second configuration blocking flow ofthe second compressed air (108) to the combustor (110).

A12. The aircraft propulsion system (100, 200, 300, 400) of paragraphA11, wherein the valve (700) comprises a sleeve valve (700) or acombustor inlet valve (700).

A13. The aircraft propulsion system (100, 200, 300, 400) of paragraphA10, further comprising a nozzle (147) directing the first exhaust gas(112) to produce a thrust (148) propelling the aircraft (900), wherein:

the nozzle (147) includes a variable core nozzle (145 a, 145 b),

the diverter (157) comprises the variable core nozzle (145 a) or avariable turbine nozzle (145 b),

the diverter is open in the first configuration to allow flow of thefirst exhaust gas (112) out of the nozzle (147) to produce the thrust(140), and

the diverter (157) is closed in the second configuration to divert theflow of the second compressed air (108) to the fuel cell (114).

A14. The aircraft propulsion system (100, 200, 300, 400) of any of theparagraphs A10-1A12, wherein the diverter (157) is positioned:

in the second compressor (104), or

downstream of the second compressor (104) and upstream of the combustor(110).

A15. The aircraft propulsion system (100, 200, 300, 400) of any of theparagraphs A10 or

A14, wherein the diverter (157) comprises an adjustable vane (814) in,or coupled to, the second compressor (104), the adjustable vane (814):

in the second configuration, diverting flow of the second compressed air(108) to the fuel (114) cell and blocking flow of the second compressedair (108) downstream to the combustor (110), and

in the first configuration, allowing flow of the second compressed air(108) downstream to the combustor (110).

A16. The aircraft propulsion system (100, 200, 300, 400) of paragraphA8, further comprising:

an engine bleed air system (500) coupled to the second compressor (104);

the second configuration further comprising the engine bleed air system(500) conveying the second compressed air (108) from the secondcompressor (104) to the fuel cell (122), or

an aircraft system (902) coupled to the engine bleed air system (500)and the engine bleed air system (500) conveying a first portion of thesecond compressed air (108) to the fuel cell (122) and a second portionof the second compressed air (108) to the aircraft system (902) forpressurizing a cabin in the aircraft (900).

A17. The aircraft propulsion system (100, 200, 300, 400) of any of theparagraphs A8-A16, further comprising:

a nacelle (128);

a fan (132) coupled to a core comprising the second compressor (104),the combustor (110), the turbine (116), and an HP turbine (116)downstream of the combustor (110);

a duct (130) between the core and the nacelle (128);

an LP electric motor (124) connected to the fuel cell (122);

a plurality of shafts including a first LP shaft (119), the shaft (118)comprising a second LP shaft (118), a first HP shaft (146), and a secondHP shaft (444);

the clutches (144) including an LP clutch (144) and an HP clutch (446);

the first configuration further comprising:

-   -   the LP clutch (144) coupling the first LP shaft (119) and the        second LP shaft (118),    -   the LP turbine (116), driven by the first exhaust gas (112),        driving the first compressor (102) and the fan (132) via the        first LP shaft (119) and the second LP shaft (118),    -   the HP clutch (446) coupling the first HP shaft (146) and the        second HP shaft (444), and    -   the HP turbine (402), driven by the first exhaust gas (112) in        the first configuration,    -   driving the second compressor (104) via the first HP shaft (146)        and the second HP shaft (444); and

the second configuration further comprising:

the LP clutch (144) dis-engaging the first LP shaft (119) and the secondLP shaft (118) and the fuel cell (122) powering the LP electric motor(124) to drive the fan (132) so that the fan (132) draws:

-   -   a first portion (134) of air (136) into the duct (130) to        generate a second exhaust (138) outputted from the duct (130),        the second exhaust (138) providing thrust (140) to an aircraft        (900) propelled using the aircraft propulsion system (100, 200,        300, 400), and    -   a second portion (142) of the air (136) into the first        compressor (102) so as to form the first compressed air (106),

the HP clutch (446) disengaging the first HP shaft (146) from the secondHP shaft (444), and the fuel cell (124) powering the HP motor (120) todrive the second compressor (104) via the first HP shaft (146).

A18. The aircraft propulsion system (100, 200, 300, 400) of any of theparagraphs A8-A17, further comprising:

a computer (1202) instructing:

activation of the first configuration during at least one of a take-offor climb of the aircraft; and

activation of the second configuration during at least one of a cruise,taxiing, descent, or landing of the aircraft.

A19. The propulsion system (100, 200, 300, 400) of any of the paragraphsA17-A18, wherein:

the fan (132) comprises a plurality of first blades and the secondcompressor (104) comprises a plurality of second blades,

a computer (1202) controls a first angular velocity of the plurality offirst blades to generate the second exhaust (138) needed for thrust(140) during cruise of the aircraft (900), and

the computer (1202) controls a second angular velocity of the secondblades so as to provide sufficient flow and pressure of the secondcompressed air (108) to the fuel cell (124) needed to generate electricpower consumed by the HP electric motor (120) and LP electric motor(124) during the cruise of the aircraft (900) powered using the secondexhaust (138).

A20. The aircraft propulsion system (100, 200, 300, 400) of paragraphA19, wherein the second compressor (104) has a number of compressionstages tailored for providing the sufficient flow.

A21. The aircraft propulsion system (100, 200, 300, 400) of any of theparagraphs A17-A20, further comprising a gearing connected to the firstLP shaft (119) between the first compressor (102) and the fan (132), thegearing adjusting a torque output of the LP electric motor (124) fordriving the fan (132) at a different speed than the first compressor(102).

A22. The aircraft propulsion system (1200) (100, 200, 300, 400) of anyof the paragraphs A1-A21, wherein the second compressor (104) comprisesat least one of a high pressure compressor or an intermediate pressurecompressor, and the first compressor (102) comprises a low pressurecompressor.

A23. An aircraft (900) comprising the aircraft propulsion system (1200)(100, 200, 300, 400) of any of the paragraphs A1-A22, further comprisinga fuel tank (150) connected to the combustor (110) and the fuel cell(122), wherein the aircraft propulsion system (100, 200, 300, 400) isconfigured to generate thrust (140) solely by reacting the fuel (114)with the second compressed air (108) in at least one of the combustor(110) or the fuel cell.

A24. The aircraft (900) of paragraph A23, wherein the fuel (114)comprises hydrogen.

A25. An aircraft propulsion system comprising:

a hydrogen powered gas turbine engine;

a fuel cell;

an electric motor electrically coupled to the fuel cell and mechanicallycoupled to a fan, and

a controller coupled to the gas turbine engine, the fuel cell, and themotor, the controller configured to supply hydrogen directly to the gasturbine engine in a first mode of operation and supply hydrogen to thefuel cell in a second mode of operation.

A26. The system of paragraph A25 wherein the fuel cell is configured tosupply electrical power to the motor during the second mode ofoperation.

A27. The system of paragraph A25 further comprising sprag clutch coupledto the motor.

A28. The system of paragraph A25 further comprising dampers to preventairflow through a portion of the gas turbine engine during the secondmode of operation.

A29. An aircraft comprising:

at least one hydrogen fuel tank; and

the propulsion system of any of the paragraphs A25-29, wherein thepropulsion system is configured to be powered solely by the hydrogen.

A30. The propulsion system of paragraph A1, wherein the secondcompressor is only driven by an electric motor and the propulsion systemdoes not include an HP clutch or an HP turbine.

A31. The propulsion system of paragraph A1, comprising a clutch andgearing comprising a gear ratio between the LP turbine and an HP shaftdriving the HP compressor.

A32. The propulsion system of any of the paragraphs A1-A31, wherein fanThrust (140) is generated by the main engine fan 132, core Thrust (148)is generated by the gas turbine exhaust during combustion only, andsupplemental thrust (159) comprises thrust recovery from the fuel cellexhaust.

A33. The aircraft propulsion system of any of the paragraphs A1-A32,further comprising the engine bleed air system (500):

coupled to at least one of the second compressor (104) or the firstcompressor (102) so as to obtain engine bleed air (550) comprising atleast a portion (516) of the second compressed air (108) or the firstcompressed air (106),

coupled to at least one of:

a low temperature heat exchanger (152) configured to cool at least aportion of the engine bleed air (550) to one or more temperaturessuitable for aircraft use on the aircraft (e.g., in an air conditioningsystem); or

a fuel heat exchanger (154) configured to transfer heat from the enginebleed air (550) to the fuel (114) comprising liquid hydrogen, so thatthe heat boils the liquid hydrogen into a gas suitable for burning inthe combustor (110) or reaction in the fuel cell (122) to generate theHP electric power.

A34. The aircraft propulsion system (100) of any of the paragraphsA1-A5, wherein:

the turbine (116) comprises the single or only turbine in the aircraftpropulsion system (100) and the propulsion system does not include anadditional HP turbine for driving the second compressor (104) and/or theturbine (116) is not sized or configured to mechanically drive thesecond compressor (104) directly via an HP shaft.

Method of Operating

FIG. 11 illustrates a method of generating thrust.

Block 1100 represents obtaining or providing a propulsor comprising ahybrid gas turbine engine, e.g., as described in any of the paragraphsA1-A

Block 1102 represents taxiing the aircraft. In one or more examples, thepropulsor (e.g., including at least one of the fan, LPC, and HPC) ispowered entirely by the fuel cell reacting a fuel (e.g., hydrogen) usingthe compressed air outputted from a compressor in the hybrid gas turbineengine.

Block 1104 represents take-off and/or climbing the aircraft. Thepropulsor is at least partially powered by the combustion of the fuel inthe combustor with compressed air to generate a first exhaust gasproviding a core thrust for an aircraft. In one example, the engineburns the fuel comprising hydrogen (or other fuel not including keroseneor a hydrocarbon fossil fuel) by channeling the hydrogen directly tointo the combustor of the core gas turbine engine. In one or moreexamples, the combustor is coupled to a turbine and the turbine iscoupled to a generator so that exhaust gas driving the turbine is usedto generate electric power useful for driving the one or morecompressors outputting the compressed air. In one or more examples, thefuel cell is used to provide supplementary power to the one or morecompressors providing compressed air to the combustor.

Block 1106 represents cruising of the aircraft, wherein the propulsor ispowered by reacting of the fuel in the fuel cell so as to generateelectricity used to power at least one of the compressors and a fangenerating the second exhaust comprising a second thrust during thecruise of the aircraft. In one or more examples, the compressor(s) andfan are powered entirely by the fuel cell.

Block 1108 represents descent and/or landing of the aircraft. In one ormore examples, the propulsor is powered by reacting of the fuel in thefuel cell so as to generate electricity used to power at least one ofthe compressors and a fan generating the second exhaust comprising asecond thrust during the descent and/or landing of the aircraft.

Block 1110 represents optional maintenance of the aircraft. In one ormore examples, the step comprises adjusting (e.g., reducing) a frequencyof maintenance of the turbines in the gas turbine engine depending onthe number of hours the turbines are operated (e.g., taking into accountthat the turbines are only used for a portion of the aircraft missionduring periods of peak demand (e.g., take-off), thereby reducing wearand tear of the turbines.

Example variations of the method include, but are not limited to, one orany combination of the following.

B1. The method wherein one or more electric motors are coupled to atleast one of the fan or one or more compressors (booster/LPC and/or HPC)via one or more clutches and the fuel cell generates the electricalpower to drive the electric motor(s) powering the at least one of thefan or the one or more compressors.

B2. The method wherein one or more diverters (e.g., dampers, valves)bypass the compressed air outputted from the HPC away from the combustorto the fuel cell during operation of the fuel cell. In one or moreexamples, HP turbine and LP turbine are shut down using a variableturbine inlet nozzle during operation of the fuel cell.

B3. The method comprising selecting the fuel cell to power the hybridgas turbine engine during one or more phases of flight (taxiing,take-off, climbing, cruising at various altitudes, and descent) tocontrol the thrust specific fuel consumption and utilize the fuel moreefficiently (taking into account that fuel cell energy conversionefficiency is higher than gas turbine fuel energy conversion). In one ormore examples, the propulsor is entirely powered by the fuel cell duringat least one of taxiing, cruising, descent or landing of the aircraft(when the combustor is switched off and the turbines are not rotating orrotating at low revolutions per minute). In one or more furtherexamples, the fuel cell provides supplemental power to the fan and orthe HPC during take-off or climbing of the aircraft. In one or moreexamples when the combustor is operating, the turbine revolutions perminute is sufficient to meet the fan and HPC power requirements.

B4. The method comprising controlling driving speed of and air flowinto, the compressors during one or more of the phases of flight (taxi,take-off, climb, cruise, or descent). In one or more examples, the LPC(booster) and HPC are operated at lower speeds and with higher flow ofair (but lower pressure) using the fuel cell, as compared to when theLPC and HPC are directly driven by a turbine, because the fuel cellcombustion reaction is different than combustor combustion reaction. Inone or more examples, the LPC and HPC are operated at the optimumrevolutions per minute for satisfying thrust output requirements fromthe fan and flow and pressure requirements for the booster and HPC. Inone or more further examples, the compressors are driven at the speedoptimized or tailored for meeting compressed air requirements of thefuel cell reacting the fuel with the compressed air (independent of therequirements of the combustor).

B5. The method comprising supplying at least one of the cabin (or airconditioning system supplying air to the cabin) with the compressed airdischarged from the compressors (e.g., HPC) during one or more of thephases of flight or taxiing.

B6. The method comprising cooling the turbine(s) when the propulsor isbeing powered entirely by the fuel cell, wherein turbine blades arecooled once fuel flow to combustor is turned off.

B7. The method wherein the fuel reacted in the combustor and the fuelcell comprises hydrogen.

B8. A method of generating thrust (140), comprising:

reacting a fuel (114) using compressed air (108) outputted from acompressor (104) in a hybrid gas turbine engine (100), wherein thereacting is used to generate an exhaust (112, 138) gas providing thrust(148, 140) for an aircraft (900), the reacting further comprising:

reacting the fuel (114) in a fuel cell (122) so as to generateelectricity used to power at least one of:

-   -   a fan (132) generating thrust (140) during a cruise of the        aircraft (900), or    -   the compressor comprising an HP compressor (108) during a        take-off of the aircraft (900); and

burning (combusting) the fuel (114) in a combustor (110) in the gasturbine engine (100) during take-off of the aircraft (900), so as togenerate the exhaust comprising exhaust gas (112) through combustion ofthe fuel (114).

B9. The method of paragraph B8, further comprising using the exhaust gas(112) to generate electric power used to drive the compressor (108)outputting compressed air (108) to the combustor (110) during a take-offof the aircraft (900).

11. Processing Environment

FIG. 12 illustrates an exemplary system 1200 used to implementprocessing elements needed to control the propulsor. In other examples,the system 1200 is a flight control system used to control the clutchesand electrical machines and circuits that power the propulsor asdescribed herein.

The computer 1202 comprises a processor 1204 (general purpose processor1206A and special purpose processor 1206B) and a memory 1206, such asrandom access memory (RAM). Generally, the computer 1202 operates undercontrol of an operating system 1208 stored in the memory 1206, andinterfaces with the user/other computers to accept inputs and commands(e.g., analog or digital signals from the crew or flight control system)and to present results through an input/output (I/O) module 1210. Thecomputer program application 1212 accesses and manipulates data storedin the memory 1206 of the computer 1202. The operating system 1208 andthe computer program 1212 are comprised of instructions which, when readand executed by the computer 1202, cause the computer 1202 to performthe operations and/or methods herein described. In one embodiment,instructions implementing the operating system 1208 and the computerprogram 1212 are tangibly embodied in the memory 1206, thereby makingone or more computer program products or articles of manufacture capableof controlling the propeller torque applied to the propeller assembly asdescribed herein. As such, the terms “article of manufacture,” “programstorage device” and “computer program product” as used herein areintended to encompass a computer program accessible from any computerreadable device or media. Also shown is a source of power 1212 for thecomputer.

Those skilled in the art will recognize many modifications may be madeto this configuration without departing from the scope of the presentdisclosure. For example, those skilled in the art will recognize thatany combination of the above components, or any number of differentcomponents, peripherals, and other devices, may be used.

CONCLUSION

This concludes the description of the preferred embodiments of thepresent disclosure. The foregoing description of the preferredembodiment has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit thedisclosure to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of rights be limited not by this detailed description,but rather by the claims appended hereto.

What is claimed is:
 1. An aircraft propulsion system comprising: a firstcompressor; a second compressor coupled to the first compressor toreceive a first compressed air outputted from the first compressor andcompress the first compressed air into a second compressed air; acombustor positioned downstream of the second compressor to receive thesecond compressed air outputted from the second compressor, thecombustor outputting a first exhaust gas formed from a fuel burned withthe second compressed air; a turbine positioned downstream of thecombustor to receive the first exhaust gas; a shaft connected to theturbine and the first compressor, the shaft transferring power from theturbine, driven by the first exhaust gas, to the first compressorforming the first compressed air; a high pressure (HP) electric motorconnected to the second compressor via a high pressure (HP) shaft, whenthe second compressor is dis-engaged from the shaft via a clutch,wherein the HP shaft is concentric about the shaft and positionedentirely upstream of the combustor; and a fuel cell connected to the HPelectric motor, the fuel cell configured to react the second compressedair with the fuel to generate HP electric power used to power the HPelectric motor driving the second compressor to form the secondcompressed air when the second compressor is dis-engaged from the shaftvia the clutch.
 2. The aircraft propulsion system of claim 1, furthercomprising: a generator connected to the shaft to generate electricpower from the power transferred from the turbine; and a circuittransmitting the electric power from the generator to the HP electricmotor to power the HP electric motor driving the second compressor. 3.An aircraft propulsion system comprising: a first compressor; a secondcompressor coupled to the first compressor to receive a first compressedair outputted from the first compressor and compress the firstcompressed air into a second compressed air; a combustor positioneddownstream of the second compressor to receive the second compressed airoutputted from the second compressor, the combustor outputting a firstexhaust gas formed from a fuel burned with the second compressed air; aturbine positioned downstream of the combustor to receive the firstexhaust gas; a shaft connected to the turbine and the first compressor,the shaft transferring power from the turbine, driven by the firstexhaust gas, to the first compressor forming the first compressed air; ahigh pressure (HP) electric motor connected to the second compressor viaa high pressure (HP) shaft, wherein the HP shaft is concentric about theshaft and positioned entirely upstream of the combustor; a fuel cellconnected to the HP electric motor, the fuel cell configured to reactthe second compressed air with the fuel to generate HP electric powerused to power the HP electric motor driving the second compressor toform the second compressed air; a nacelle; a duct between a core and thenacelle, the core comprising the second compressor, the combustor, andthe turbine; a fan coupled to the first compressor and the duct to draw:a first portion of air into the duct to generate a second exhaustoutputted from the duct, the second exhaust providing a thrust for anaircraft propelled using the aircraft propulsion system, and a secondportion of the air into the first compressor, wherein the firstcompressor compresses the second portion of the air to form the firstcompressed air inputted to the second compressor meeting the secondcompressor to the shaft in a first configuration when the turbine secondcompressor via the shaft; and a clutch: connecting the second compressorto the shaft in a first configuration when the turbine drives the secondcompressor via the shaft; and dis-engaging the shaft from the secondcompressor in a second configuration.
 4. The aircraft propulsion systemof claim 3, further comprising: a low pressure (LP) electric motor; afirst low pressure (LP) shaft connected to the fan and the firstcompressor; the shaft comprising a second low pressure (LP) shaft; an LPclutch connected to the second LP shaft and the first LP shaft; and thefirst configuration further comprising the combustor burning the fuel toform the first exhaust gas and the LP clutch connecting the first LPshaft to the second LP shaft so that the first LP shaft and the secondLP shaft transfer the power from the turbine, driven by the firstexhaust gas, to the first compressor and the fan; and the secondconfiguration comprising the fuel cell reacting the fuel with the secondcompressed air, the LP clutch disengaging the first LP shaft from thesecond LP shaft, and the LP electric motor driving the fan and the firstcompressor via the first LP shaft.
 5. The aircraft propulsion system ofclaim 4, further comprising: one or more circuits; and a computer systeminstructing: activation of the second configuration during a cruise ofthe aircraft, the second configuration further comprising the one ormore circuits electrically connecting the LP electric motor to the fuelcell and the fuel cell powering the LP electric motor via the one ormore circuits, and activation of the first configuration during atake-off of the aircraft.
 6. The aircraft propulsion system of claim 1,further comprising: the clutch comprising an LP-HP clutch: connectingthe second compressor in the first configuration to the shaft during atake-off of an aircraft propelled using the aircraft propulsion system;and dis-engaging the shaft from the second compressor in the secondconfiguration during a cruise of the aircraft.
 7. The aircraftpropulsion system of claim 6, further comprising a gearing connected tothe second compressor to adjust a torque output of the turbinetransferred to the second compressor.
 8. An aircraft propulsion system,comprising: a first compressor, a second compressor coupled to the firstcompressor to receive a first compressed air outputted from the firstcompressor and compress the first compressed air into a secondcompressed air; a combustor positioned downstream of the secondcompressor to receive the second compressed air outputted from thesecond compressor, the combustor outputting a first exhaust gas formedfrom a fuel burned with the second compressed air; a turbine positioneddownstream of the combustor to receive the first exhaust gas; a shaftconnected to the turbine and the first compressor, the shafttransferring power from the turbine, driven by the first exhaust gas, tothe first compressor forming the first compressed air; an HP electricmotor connected to the second compressor; and a fuel cell connected tothe HP electric motor, the fuel cell configured to react the secondcompressed air with the fuel to generate HP electric power used to powerthe HP electric motor driving the second compressor via the second shaftto form the second compressed air; and one or more clutches:dis-engaging at least one of the first compressor or the secondcompressor from the shaft in a first configuration, the firstconfiguration further comprising: the fuel cell reacting the fuel withthe second compressed air to generate the HP electric power powering theHP electric motor driving the second compressor, and the combustor notoutputting an amount of the first exhaust gas sufficient to generatethrust propelling an aircraft coupled to the aircraft propulsion system;coupling at least one of the first compressor or the second compressorto the shaft in a second configuration further comprising: the combustorburning the fuel with the second compressed air to generate the firstexhaust gas driving the turbine and the turbine driving the secondcompressor via the shaft.
 9. The aircraft propulsion system of claim 8,wherein each of the clutches comprise a sprag clutch.
 10. The aircraftpropulsion system of claim 9, further comprising: a diverter regulatingflow of the second compressed air outputted from the second compressorinto the combustor or the fuel cell.
 11. The aircraft propulsion systemof claim 10, wherein: the diverter comprises a valve connected to atleast one of the second compressor or the combustor, the valve is openin the first configuration allowing output of the second compressed airto the combustor, and the valve is closed in the second configurationblocking flow of the second compressed air to the combustor.
 12. Theaircraft propulsion system of claim 11, wherein the valve comprises asleeve valve or a combustor inlet valve.
 13. The aircraft propulsionsystem of claim 10, further comprising a nozzle directing the firstexhaust gas to produce the thrust propelling the aircraft, wherein: thenozzle includes a variable core nozzle, the diverter comprises thevariable core nozzle or a variable turbine nozzle, the diverter is openin the first configuration to allow flow of the first exhaust gas out ofthe nozzle to produce the thrust, and the diverter is closed in thesecond configuration to divert the flow of the second compressed air tothe fuel cell.
 14. The aircraft propulsion system of claim 10, whereinthe diverter is positioned: in the second compressor, or downstream ofthe second compressor and upstream of the combustor.
 15. The aircraftpropulsion system of claim 10, wherein the diverter comprises anadjustable vane in, or coupled to, the second compressor, the adjustablevane: in the second configuration, diverting flow of the secondcompressed air to the fuel cell and blocking flow of the secondcompressed air downstream to the combustor, and in the firstconfiguration, allowing flow of the second compressed air downstream tothe combustor.
 16. The aircraft propulsion system of claim 10, furthercomprising: a nacelle; a fan coupled to a core comprising the secondcompressor, the combustor, the turbine, and an HP turbine downstream ofthe combustor; a duct between the core and the nacelle; an LP electricmotor connected to the fuel cell; a plurality of drive shafts includinga first LP shaft, the shaft comprising a second LP shaft, a first HPshaft, and a second HP shaft; the clutches including an LP clutch and anHP clutch; the first configuration further comprising: the LP clutchcoupling the first LP shaft and the second LP shaft, the turbinecomprising an LP turbine, driven by the first exhaust gas, driving thefirst compressor and the fan via the first LP shaft and the second LPshaft, the HP clutch coupling the first HP shaft and the second HPshaft, and the HP turbine, driven by the first exhaust gas in the firstconfiguration, driving the second compressor via the first HP shaft andthe second HP shaft; and the second configuration further comprising:the LP clutch dis-engaging the first LP shaft and the second LP shaftand the fuel cell powering the LP electric motor to drive the fan sothat the fan draws: a first portion of air into the duct to generate asecond exhaust outputted from the duct, the second exhaust providing thethrust to the aircraft propelled using the aircraft propulsion system,and a second portion of the air into the first compressor so as to formthe first compressed air, the HP clutch disengaging the first HP shaftfrom the second HP shaft, and the fuel cell powering the HP electricmotor to drive the second compressor via the first HP shaft.
 17. Theaircraft propulsion system of claim 16, further comprising: a computerinstructing: activation of the first configuration during at least oneof a take-off or climb of the aircraft; and activation of the secondconfiguration during at least one of a cruise, taxiing, descent, orlanding of the aircraft.
 18. The aircraft propulsion system of claim 16,wherein: the fan comprises a plurality of first blades and the secondcompressor comprises a plurality of second blades, a computer controls afirst angular velocity of the plurality of first blades to generate thesecond exhaust needed for the thrust during cruise of the aircraft, andthe computer controls a second angular velocity of the second blades soas to provide sufficient flow and pressure of the second compressed airto the fuel cell needed to generate the HP electric power consumed bythe HP motor and the LP electric motor during the cruise of the aircraftpowered using the second exhaust.
 19. The aircraft propulsion system ofclaim 9, further comprising: an engine bleed air system coupled to thesecond compressor, the second configuration further comprising theengine bleed air system conveying the second compressed air from thesecond compressor to the fuel cell, or an aircraft system coupled to theengine bleed air system and the engine bleed air system conveying afirst portion of the second compressed air to the fuel cell and a secondportion of the second compressed air to the aircraft system forpressurizing a cabin in the aircraft.
 20. The aircraft propulsion systemof claim 19, further comprising the engine bleed air system: coupled toat least one of the second compressor or the first compressor so as toobtain engine bleed air comprising at least a portion of the secondcompressed air or the first compressed air, coupled to at least one of:a low temperature heat exchanger configured to cool at least a portionof the engine bleed air to one or more temperatures suitable foraircraft use; or a fuel heat exchanger configured to transfer heat fromthe engine bleed air to the fuel comprising liquid hydrogen, so that theheat boils the liquid hydrogen into a gas suitable for burning in thecombustor or reaction in the fuel cell to generate the HP electricpower.